The present invention relates to an image capture system and an omnidirectional image capture system in particular, and to an imaging optical system used therein.
As image capture systems which “simultaneously take an image” in omnidirections, those using two wide-angle lenses are known (refer to Japanese Patent Application Publication Number 2010-271675 and Japanese Patent Number 3290993).
Such an omnidirectional image capture system can simultaneously acquire image information in all directions (in a solid angle of 4π radian), and therefore can be effectively used for a security monitoring camera, a vehicle-mounted camera, or the like.
For example, for coverage of news and the like, extremely accurate and fair image information can be recorded by using a small-sized omnidirectional image capture system in a “hand-held condition”.
An image of a weather state in the ominidirections can be taken and applied to an analysis for weather information.
In addition, an image of landscape information can be taken and applied to the use in advertisement and promotion of the art field.
In such an image capture system, two wide-angle lenses each having a field angle exceeding 180 degrees (what is called a “fisheye lens”) are used in combination.
Images taken by the respective wide-angle lenses are converted into electric signals by the same or individual imaging device and the electric signals are processed, so that an image in the omnidirections can be taken.
Neither of Japanese Patent Application Publication Number 2010-271675, and Japanese Patent Number 3290993 disclose the specific configuration of the wide-angle lens itself.
Moreover, in the image capture systems described in these patent documents and the like, each image formation light flux by each of the imaging optical systems is guided to an imaging device by an individual light-guide device (route changing device or reflection optical equipment).
As described above, because the light-guide device is used for each wide-angle lens, it is difficult to reduce a “distance between maximum field angles” of the two wide-angle lenses. The “distance between maximum field angles” will be described later.
When two wide-angle lenses each having a field angle exceeding 180 degrees are combined, a space portion where maximum field angle light fluxes entering the respective wide-angle lenses are not overlapped with each other is present.
An image of an object present in the “space portion where maximum field angle light fluxes entering the respective wide-angle lenses are not overlapped with each other” cannot be taken.
The “space portion” is hereinafter referred to as “imaging impossible space portion”. It is needless to say that the imaging impossible space portion is preferably as small as possible.
It is difficult to reduce the imaging impossible space portion with the larger “distance between maximum field angles” mentioned above.
The larger field angles of the two wide-angle lenses to be combined are required for the reduced imaging impossible space portion in the image capture system having a larger distance between maximum field angles. This results in the severe design condition of lenses.
Moreover, with respect to an object which can be taken therein, parallaxes of an object in a maximum field angle and an object in an infinite distance differ. This results in a lager shift on the imaging element. This point also will be described later.
Japanese Patent Application Publication Number 2010-271675, and Japanese Patent Number 3290993 do not describe the specific configuration of the wide-angle lens, and not disclose such a problem of the imaging impossible space portion or a problem in parallax at all.